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How does a tiltrotor yaw while in vertical flight?
Conventional helicopters have a tail rotor or equivalent to counteract rotor torque. The pilot's rudder pedals control the force generated by the tail rotor (e.g. by changing its pitch).
But the V-22 Osprey lacks a tail rotor: it has rudders on its twin vertical stabilisers. Rudders wouldn't seem to have any useful effect when in vertical flight, because there's no horizontal airflow for them to deflect. The AW609 appears to lack even a rudder, in the photographs I've seen: the vertical stabiliser appears to be one piece in a fixed shape.
Co-axial helicopters such as the Ka-50 can yaw by varying the torque of one rotor compared to the other, but it seems unlikely to me that the same mechanism would work well when the two rotors are at opposite ends of the wings. The effect of differential torque would be much smaller, and it would have huge secondary effects (such as adverse roll). For that reason I don't think the Osprey can work that way.
So what mechanism controls the yaw on a tiltrotor?

"The effect of differential torque would be much smaller, and it would have huge secondary effects" - You're right about the secondary effects, but the effect of the diffential torque would be the same as if the rotors were coaxial.  A torque is a torque, no matter where it is "applied".

How does a Chinook yaw?  Same method...

The V22 Osprey yaws by tilting one rotor backwards from the vertical and one forward by moving the swashplate up on one side and down on the other causing a cyclic change to the rotor blade angles of attack.  This is accomplished using the pedals in just the same way as a helicopter.
Since the rotors are tilted from the vertical, this introduces a horizontal component to the thrust vector.  The rearwards titled rotor produces a horizontal thrust component to the rear and the forwards tilted rotor produces a horizontal thrust component to the front.  This produces a turning moment, using the wings as the lever, around the centre of gravity and therefore the aircraft yaws.
The secondary effects will be as expected.  Since some of the thrust vector is no longer vertical, a little more power will be required to maintain height and I expect that there will be a pitch change although I'm not familiar enough with the aerodynamics of this type to figure out which way and how big.

Tilting one rotor back while the other one forward makes sense to me, also, you mentioned correctly that this will result in loss of total lift, but tilting the engines has nothing to do with the swash plate, I don`t agree on that one. The swash plates will be used for cyclic and pitchcollective, tilting the entire aircraft back and foth, as well as increasing or decreasing total lift.

I have question in here, I asked, how such this Bell V-280 Valor (look similar to V-22 Osprey), how does it make side move when it is being hover?


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How do the Tiger Moth's anti-spin strakes work?
As originally designed, the DH.82 Tiger Moth had unpredictable spin characteristics. Many aircraft were lost because spin recovery took too long (i.e. too much loss of height). Many examples of the type have been retrofitted with anti-spin strakes, which extend forward along the top of the fuselage from the empennage. It's shown here on two DH.82a's.

The anti-spin strakes don't prevent spinning completely, but they make the spin more manageable and more predictable. Some operators of the type nowadays haven't added the strakes, because they have found their aircraft to behave itself in the spin even unmodified. There's a theory that the unpredictability of the type was the result of variations in material and construction quality in wartime.
How do the strakes help? What aerodynamic effect causes them to help spin recovery?

Here's another picture from above:
http://www.rcmf.co.uk/4um/index.php?PHPSESSID=s2hg1s91q707de0o7c3260ofq0&action=dlattach;topic=45390.0;attach=22230;image

On a totally unrelated note, the aeroplane on the left side of the photo, G-AOEI has an interesting history if you are interested in that sort of things. Both of the aeroplanes, G-AOEI and G-AHIZ belong to the Cambridge Flying Group. Here is another view of the anti-spin strakes: https://imgur.com/a/E0kJc7P

The vertical tail of the Tiger Moth is located a bit aft of the horizontal tail due to its sweep, such that the vertical will be in the wake of the root of the horizontal in a typical spin attitude (around 45° angle of attack). I would strongly recommend to fit the aluminium anti-spin strakes - those pilots who had no problem without them flew the Moth at a forward location of the center of gravity, which helps to end the spin. A lighter forward passenger/pilot will make the aircraft behave a lot differently; in spins small differences can translate in a markedly changed spin behavior.

Cut-away drawing of the Tiger Moth's tail. The anti-spin strakes are the parts marked 16.
A spin can be ended in two ways: Either the rotation rate is stopped by neutral rudder or a rudder deflection against the spin, or the separated flow on the wing is reduced by pitching down. The first way works better for aircraft with long fuselages and low wing span, and the second is preferred in aircraft with big wings like gliders. In the end, a combination of both works best and some aircraft need their own technique to end a spin safely.
Generally, it helps to have as much of the vertical tail exposed to undisturbed airflow as possible. Ventral fins are a tremendous help in upright spins but useless in inverted spins. Strakes or fillets ahead of the vertical tail are very effective, especially in fast spins when the angle of sideslip at the tail is high. In the 1930s, Arado in Germany built a range of airplanes where the vertical tail was positioned ahead of the horizontal tail, for the express purpose of making spins easier to end.

Arado 79 in flight (picture source)
The anti-spin strakes produce a vortex at high angle of attack, similar to that on a delta wing. This increases the dynamic pressure on the vertical tail and makes it more effective. Since every bit helps and the spinning characteristics can vary strongly with c.g. position, it would be careless to leave them off.

On this homebuilt aircraft site I found the following:

There are several mechanisms available for improving controllability in a spin. One is as described above, where a triangular surface is
  placed (in a horizontal attitude) at the root of the horizontal stab.
  Practical examples of this can be seen on BD-5s and the Glastar. As
  was surmised above, for local angles of attack higher than normal, the
  strake creates a vortex which provides the airplane with additional
  stab and elevator control, helping the airplane maintain a nose low
  attitude for recovery.
A similar and more common addition is the dorsal fin - a triangular
  strake placed in front of the vertical stab. This was an effective fix
  (although not a cure) for the spin characteristics of the Grumman line
  of airplanes, which also tended to flatten out. As the plane spins,
  this strake also generates a vortex flow that is imposed onto the stab
  and rudder, thus providing a force counter to the spin direction.
The last option is rarely used but it is the addition of ventral fins
  at the aft end of the body. They serve two functions - they provide
  more aft body area thus resulting in slightly better yaw damping and
  stability and also, when in a spin they create countering lift,
  similar to that of the dorsal.
None of these are fixes - they are aids for better control and for
  providing the pilot with more control authority for getting out of an
  established spin.

Although it's not really an authoritive source, it sounds like a sound explanation to me. I can image that the vortex coming from the strake helps to maintain yaw authority with the rudder.
As such it's an alternative to the dorsal fin, which you can still see on current aircraft.
However, Here the user pontifex mentions from first hand experience that there's hardly any difference:

I have been lucky enough to fly and teach on many training aircraft and have spun them all many, many times. I have never had any problems in recovering when using the advertised technique. Some had strakes, some didn't. Never noticed any difference. That also goes for the Chipmunk of which I have flown both versions.

Interestingly, the Australian authorities, military and civilian have never made the strakes mandatory here. There were hundreds of them around after the war and there still are many, all without strakes.
I found it to be a very good upright spinning aeroplane myself, solo and two up, without strakes.

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How do you choose a feature to line up on when approaching to land?
I've been taught that when I'm on final approach to land, I should pick a feature or landmark that's some distance along the extended centre-line, so that when I'm close enough to the ground that I can't properly see the runway edges any more, I can still look forwards and check my heading against this landmark. This is necessary on aircraft without flaps where the nose (the engine cowling) restricts the pilot's view of the runway in the approach.
The view along the runway changes completely from circuit height to runway level, and it's not obvious which features will be visible from less than 100 ft height. At my home aerodrome, it's easy to learn which feature to line up on, because I've seen them all before many times. When I'm landing at a new aerodrome, how can I select a feature to line up and be reasonably confident that it's still visually obvious all the way through the landing?

When I first read the title I was thinking, "Well, the runway is usually a good choice." :) Interesting question, though!

Probably the best thing to do is to start looking for your reference as you start to lose the runway under your nose. Hopefully at that point you'll be low enough to identify something that will stand out from the crowd all the way down to the ground. You may also favor choosing something closer in from the horizon at 2000AGL, to ensure you don't lose it behind the horizon as you descend. For me, flying out of Addison, it's pretty easy; the runway faces downtown Addison about 3 miles south-southeast (a row of corporate headquarters buildings along the Dallas North Tollway) which is far enough out to line up on but close enough and tall enough you'll see it right up until you pass the numbers. Flying into a more rural strip, you might have more trouble identifying a good reference that you can keep in sight as you descend.
Some potential issues with this general strategy:

Your reference point will lie well beyond the runway by design. Don't fixate on it; that will cause you to subconsciously stay higher than your intended glide path as you fly toward your reference, potentially overshooting the runway.
Your reference is a single point. That point and your aircraft make a line, which you want to be colinear with the runway. But, your aircraft is a moving point, so it's not necessarily true that you'll be in line with the runway even if your nose is on the reference point. Instead of one reference point, I'd pick two (even if they're not perfectly in line) and focus on keeping both reference points steady relative to each other.
If you can't see the runway, you may not be able to see surrounding visual aids like the glide slope indicators, which are just as important as staying lined up. Addison's PAPI lights are off to the right when approaching runway 15, which is stupid as my instructor can see them perfectly while I'm blind unless I nose down every few seconds to keep track (not an option without flaps).

While I wouldn't rely on it completely in VMC, if you have a VOR receiver aboard and the runway has an instrument approach, you can tune into the ILS frequency and use the "cross" alongside visual references to manage your approach during the time the runway is hidden from view. The ILS system is pretty well-standardized, while the visual references at each airport are not, so if you become accustomed to an ILS-augmented visual landing, the basic procedure can be applied to any airport.
The reasons I wouldn't rely totally on it include:

You're not instrument-rated (unless you are) so flying with your head in the gauges can easily kill you. Glance at it to ensure you're where you think you are, but rely on your visual references whenever you can.
You're not flying a pure instrument approach under IFR, so you still have to "see and avoid" even if you have tower staff spacing traffic around you (unless you ask for a "pop-up" instrument approach, effectively switching from VFR to IFR).
ILS availability/accuracy is not guaranteed in daytime VMC because the ILS critical areas are not required to be protected during these times. If you tell the tower what you're doing, they can advise ground traffic to use the ILS holds, but there may already be traffic in an ILS critical area and if so there's little the tower can do.
ILS may contradict visual indicators to varying degrees, because the ILS glideslope is projected from a different point along the runway than the PAPI/VASI array. You therefore shouldn't expect the ILS cross to be perfectly centered along the same path that gives you two white PAPI lights.
Radio-based ILS isn't available at every airstrip. In such cases you simply must fly a purely visual approach, and having relied on ILS to give you the proper glide slope instead of developing your sight picture will prove to be a crutch in such situations.

You don't need to worry about over-relying on ILS: the aircraft I'm flying has neither ILS nor VOR.

Dan Hulme's technique is basically the same as mine.  Keep that reference point in view at a point along an imaginary horizontal line which crosses your windscreen, controlling that position with right-left heading changes to compensate for wind.  When getting to near-touchdown altitude you can generally see out to the the side if you are more-or-less equidistant from the edges of the runway, which helps keep you on or near the centerline.
Just make sure that your initial visual "reference point" isn't a moving object, such as a cloud, a truck on the freeway... or another airplane in the sky!

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FAA requirement for recording aircraft time
I am familiar with aircraft which use a Hobbs meter for timekeeping using an oil pressure switch.  I am also familiar with aircraft with a recording tachometer.
Less familiar are aircraft which use only a hobbs or similar timekeeping device.
What are the requirement for timekeeping on aircraft with a US airworthiness certificate?  Is there a part 23 or other requirement?

Some of the questions touch the topic, but I'm afraid none to date give a satisfactory citation.  Requirements are inferred, but the need for a timekeeping device is ambiguous.  As far as I have found, the requirements of FAR 91.409(b), as well as other requirements, could be met by fastidious manual timekeeping.

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Don't all airspeeds change with weight?
Ok, so I'm a student pilot, and I'm going over the Vx, Vy, Vne, ... etc., and I see that "maneuvering speed" (the speed at which you can safely apply full flight controls) "changes with weight".
Which airspeeds don't change with weight? I can pretty much guarantee the the takeoff speed changes with weight, as would flap operating speeds, never exceed speed, and cautionary zone, because that is just the basic application of physics (inertia).
Why do we treat maneuvering speed as the only variable airspeed?

Your instinct is correct; almost all of the key airspeeds — those at which something special happens aerodynamically — vary with weight.
There's a distinction, though, between "speeds at which something special happens aerodynamically" and "regulatory limiting speeds that prevent you from doing something bad."
For example, VNE is a regulatory value; it is prohibited to exceed this speed at any weight. This value includes a safety margin and is determined from flight test data. Nothing special happens aerodynamically at the published VNE speed. (Thank goodness!) The special stuff, like aeroelastic flutter or structural failure, happens at some speed well above VNE, regardless of your weight (as long as it's within the allowable CG envelope of course).
Another example, VFE, is similar. Nothing special happens at this speed. It's just a safety value: as long as you're below this speed, you won't tear the flaps off the plane if you extend them, regardless of your weight.
Almost all speeds that aren't "regulatory limits" do indeed change with weight. Some examples:

VA design maneuvering speed
VX best angle of climb speed
VY best rate of climb speed
VR rotation speed
VS0 landing configuration stall speed
VS1 "specific" configuration stall speed

For larger multi-engine airplanes that you'll encounter later in your flying career:

V1 engine failure recognition speed (or takeoff decision speed)
V2 takeoff safety speed
VMC minimum control speed

(Note that a lot more factors besides just weight can go into these latter speeds, such as atmospheric conditions and reduced-thrust takeoffs.)
For small airplanes, it is common to publish these speeds as single values, measured at gross weight. For many of them there are also graphs in the performance section that show you how the actual speed varies with weight.
For larger aircraft, the performance graphs (or calculations) are always used. For example, you won't use a single "stall speed" value from a handy table in the "POH" of a 747. In these types of aircraft, key numbers are calculated as needed on each flight for current weight.

To explain why these speeds change with weight:
VA design maneuvering speed: this is because it takes a lot more force to move a heavy plane than it does a lighter plane. On a lighter plane, the surfaces deflect, apply a force, and the plane moves. Once the plane is moving, the surfaces move too, which lessens the force on them. A heavier plane will move less, which means the surfaces are applying more force and for longer to move the plane the same amount.
VX best angle of climb speed
VY best rate of climb speed: A heavier plane will need to produce more lift, and therefore have more drag, which affects climb performance.
VR rotation speed
VS0 landing configuration stall speed
VS1 "specific" configuration stall speed: A heavier plane needs more airspeed to produce enough lift to take off or not stall. Here is why:
Among other things, lift is dependent on speed and angle of attack. So at a given speed, angle of attack can increase to generate more lift. The plane will have a maximum angle of attack above which it will stall. Since these are minimum speeds, they are at the maximum angle of attack, so speed must increase to provide the lift.

Well, top of my head: Vtyre and MMO are two speeds which are totally independent of aircraft mass. The first is simply a tyre speed limitation and the second is aerodynamically determined by the wing. The rest should all change one way or another with mass.
Why then use single values for most of these speeds? Well, for one thing, in smaller aircraft, those changes will ammount to 1,2 maybe 5 knots from Basic Empty Mass to Maximum Take Off Mass, so memorizing your stall speed as variable between 39 to 41.2 knots (when you have about +/- 5 kts accuracy on the airspeed indicator anyway) is pointless. Round it up to 45 and stay above that. Remember that most of these "fixed" speeds are CAS while some are EAS (and remember how that influences things), then remember those speeds will change from flight to flight depending on weight, but not too much.
As you get into slightly bigger airplanes you will start seeing the AFM giving 2 or 3 sets of speeds for different weights (850 kg, 1000kg, 1150kg) and it is your job to know them and interpolate them for today's weight.


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How are practice areas communicated?
When I fly near my local airport (KSSF) in San Antonio, there's a designated South Practice Area and North Practice Area. ATC knows where they are and all the flight schools at the airport seem to have a common idea of their boundaries.
However, they aren't marked anywhere on charts or supplements and I can't seem to find any information online. I was wondering how these are communicated between different entities (control towers, ARTCCs, flight schools) - are they standardized at all? Is there anywhere I can find information?

Based on my personal experience, the established (and apparently FAA-sanctioned) procedure is to get on the glider frequency 123.5 and constantly call out your location every couple of minutes, much to the annoyance of every glider pilot within radio range.

Some practice areas are charted, e.g. there's one near Hillsboro, OR. The VFR sectional has this note just northwest of the Newberg VOR:

If you then look up the Chart Supplement, there are more details on the area and the frequency to use:

Note that 122.75 is the general air-to-air frequency for the US, it isn't a specific frequency for that area.
Having said that, many practice areas are informal and they rely on local knowledge. That could be a documented agreement between ATC and flight schools, or an informal arrangement between local instructors. I have no idea who determines which areas are worth charting.
As far as I know, there's no specific regulation or central FAA control of practice areas, with the exception of aerobatic practice areas.


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How is the helicopter throttle control connected to the transmission system?
Both the throttle control and the transmission system regulate the rotor blade RPM but how are they connected to each other or are they different from each other.

The transmission is just a transmission. It doesn't regulate speed.  It's not like a car; there is only one gear ratio and the only clutch is a sprag clutch that lets it freewheel when power is removed.

Can you perhaps clarify what you think the impact of the Transmission is?

Typically (in the case of piston-engined helicopters) the throttle isn’t connected to anything except the carburettor of the engine.  It’s immediate function is to restrict the amount of air getting into the cylinders, indirectly the amount of fuel and the power output of the engine, and this combines with rotor pitch etc to determine rotor speed and ultimately lift.

The transmission ratio is designed to get the best operating speed for the main rotor to coincide with the best power operating point for the engine. This is done by choosing the amount of gear-down to, for example, obtain 800 RPM on the main rotor while the engine is governed to run at 2400 RPM.
Then, when the pilot pulls up on the collective, the governor (if the helo has one) commands the throttle to maintain 2400 engine RPM as the main rotor torque load increases- and the helo takes off with the engine running at 2400 RPM, at the peak of its power curve (or near it). Otherwise the pilot advances the throttle manually to maintain rotor speed.

@jim, will edit.


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What happens when you break the rules while flying?
In a car, when you speed, you get pulled over, probably get a ticket, and you might get points added to your license.
How are air traffic rules enforced? Are there patrol planes that make sure no one is going over the speed limit? I have always been curious about that.

Radar is a bit more widespread (eg can hit more than just 1 vehicle) in controlled airspace.

Ok... what do you mean?

In a car, when you speed, you get pulled over...where I come from, in a car when you speed, 99% of the time, you get to where you're going faster.

Speed will seldomly be a problem.  Restricted and/or controlled airspace violations are much more relevant.

@flyingfisch - rather than having to be close to you, actually on the road, checking their radar, in the air, the radar is omnidirectional and with a much greater range. Plus, they can hit multiple aircraft at once with radar

@SSumner: ah ok.

When you break the rules while flying, it falls into one of two categories:

Only you know about it
The FAA knows about it

In either case, the very first thing you do is file a NASA ASRS form.  You might ask, why does NASA care about airplanes?  They are acting as an uninterested 3rd party to your actions, and collate statistics from this information.  If the FAA becomes aware of your actions, the presence of an ASRS form in many cases limits the action the FAA can take against you.  It is always worth filling out and I have filled out a few myself.
In the case the FAA knows about it, how do they know about it?  This typically happens when you are in radar control and do something wrong or are on the ground and do something wrong.
Some examples of this are:

Flight plan in the FMS is incorrect and you make a turn off of your cleared course.  The controller will see this.
You taxi incorrectly
Runway incursion
Climb / descend through your cleared altitude

In most of these cases, the controller will just correct you.  In cases that result in a loss of separation or a runway incursion, you may get a phone number from the controller to call when you land.
Less commonly, something you do may be witnessed by an FAA inspector -- you buzzed the tower when he was on the ramp watching you.  Or perhaps he watched you get into a plane and fly off without performing a pre-flight inspection.  Perhaps you were ramp checked and something wasn't right with you or the airplane.
In all of the above cases, if you are able to file an ASRS form, do it.  If you do something that may be severe and are a member of AOPA, call their legal team and discuss the situation.
If the FAA responds to something they know about, it can range from a controller talking to you over the phone up to certificate action (suspension, revoked) to the infamous "709 ride", in which the FSDO administers a checkride and decides which, if any, ratings you keep and which you lose.

It is the National Aeronautics and Space Administration. It is a good observation though that many people think NASA is only about space.

Did you get caught? If yes, you face enforcement action. Maybe a fine, maybe a revocaation or suspension of your certificate for a while, maybe jail time. If no, you might feel guilty enough to send in an ASRS form. This greatly decreases your chances of getting punished later if someone finds out, unless they also find out you intentionally broke the rules.
Honestly, there are a ton of rules in aviation but they're enforced by a fairly small agency who isn't even that vigilant when it comes to the little guys. Kind of the opposite of the police on the ground. But in all, it's pretty easy to do almost whatever you want and not even break a rule. Use common sense to stay safe and usually you're within the law in the air.


text:
Cost for teletype type B (TTY) message exchange over SITA network
Does anyone know which party (sender or receiver) bears the cost of sending TTY messages over the SITA network that are commonly used between airlines, GDSs and different vendors. Thanks.


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Why can the rear rotors of helicopters move freely in this direction?
As you can see in the video in the imgur link  below i recorded a video of the Alouette 2 rear tail rotor and as you can see it moves freely in that direction. Why does it freely move in that direction, what is the purpose? Also just to clarify this is a different movement than when you press the pedals in the cockpit. when i used the pedals in the cockpit it moved the rear rotor in a different way than this, this is different than that. Is the purpose of this movement so that when there is an unexpected load on the rear rotor it can freely move and decrease the total amount of load absorbed by the rotor and lengthen the life of the rotor?
https://i.sstatic.net/Bjosn.jpg

Those are flapping hinges that give the blade some freedom of movement in the flapping axis, to accommodate the variations in lift of the blade as it moves around while the machine is moving forward. It's the same function as the flapping hinges in the main rotor, but without the disc tilting function provided by the swashplate (as if the swashplate was fixed at neutral).
Having no swash plate, the geometric angle commanded by the input linkage of the blade is constant going around. The advancing blade that gets increased lift wants to flap "out", and the retreating blade that gets decreased lift wants to flap "in" to accommodate the increase and decrease of blade tip speed through the air while moving forward. The hinge accommodates that flapping motion.
There's also usually a geometric relationship built into blade's pitch change horn and the flapping axis itself that causes blade angle to decrease slightly when the blade flaps out from increased lift, and increase slightly when the blade flaps in from decreased lift. This reduces the amount of actual flapping movement required because the slight blade angle change induced by the flapping movement partially cancels out some of the lift change caused by the velocity change.


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Why does the torque curve of free shaft gas turbines keep gradually dropping as RPMs increase?
When i look at the output shaft torque curve of a free shaft gas turbine i can see that they are almost like an electric motor. It makes peak torque at very low rpm and then torque keeps gradually dropping. I know that in electric motors the torque drops due to back EMF as RPMs increase. In free shaft gas turbines, what causes this torque decrease as RPMs increase? For example the curve for AGT1500

Let's start with this example:
Start up the turbine with no load connected to the shaft, then advance the fuel flow rate to the maximum allowable value. The output shaft will achieve some (very high) RPM after a short while, at which the speed of the turbine blade tips starts getting close to the speed of the gas flowing through the turbine disc. In this condition, the ability of the blades to extract useful work from the gas flow falls off towards zero, and so the torque output of the turbine disc falls off towards zero too.


text:
Are walkalong gliders based on the principles of ground effect?
Does a walkalong glider stay aloft because of ground effect (caused by the paddle), or for some other reason?

The article you linked answers your question: "Ground effect should not be confused with ridge lift when explaining how walkalong gliders stay up. Ground effect involves a horizontal surface. Ridge lift requires a sloping surface. In ground effect the air does not have to move relative to the ground whereas ridge lift requires the wind to be blowing horizontally against the ridge. Walkalong gliders are sustained and controlled in the ridge lift produced by the moving paddle."

No the paddle acts as an inverted wing and pushes air up, this in turn will push the glider up.
Even with ground effect a non-powered glider cannot maintain height and speed.

The glider is just a glider.  The paddle generates lifting force, essentially creating a moving updraft underneath the glider, which keeps it in the air.
Ground effect reduces drag, but doesn't create lift.  As ratchet freak mentioned, ground effect alone is not enough to keep a glider in the air indefinitely.


text:
Denver International Airport pneumatic tube systems
Wikipedia says:

Denver International Airport uses many pneumatic tube systems, including a 25 cm diameter system for moving aircraft parts to remote concourses, a 10 cm system for United Airlines ticketing, and a robust system in the parking toll collection system with an outlet at every booth.

Note: No citation, and I can't find any reference to it on the web.
Question: If these systems actually exist, what are their total lengthes (eg. 35 km total) and usage rate (eg. 7000 objects per day)?
References appreciated.

(asked after asking whether it is on-topic on meta: https://aviation.meta.stackexchange.com/questions/3630/would-a-question-about-a-system-that-i-am-not-sure-actually-exists-be-on-topic)

There’s a bit of info here: http://www.expo1000.com/parking/press/20000322.htm mainly about the cash handling system for the toll booths, but it says all the systems were built by the same company.

Have you considered just asking Denver Airport on Twitter, or whatever their preferred social media platform is? There are a few web references from when the airport was about to open (here, here) but nothing recent, and the provider's site doesn't mention the airport at all. It looks like the system certainly was there, but I can't find any recent link that confirms it still is there.

@Pondlife we don't really want to send people away, do we?

@Federico No, but it's a good option if no one here can find a clear reference. And if the OP does ask them, he can always come back and answer his own question.

So we should ask on Twitter and then answer here? That's silly. :)

Not a pneumatic system, but "The automated system was an underground, computer-driven railroad network for moving baggage. But bags were misdelivered, luggage was chewed up and cars derailed and jammed tracks. The system was responsible for repeated delays in the opening of DIA, which began operating in 1995". There are some studies on this failure, e.g. this one and this one. 27 km. (17 miles) and 4000 radio-controlled carts

I asked DIA by email.

According to the Public Relations Department at the Denver International Airport, as of May 24, 2019 there is no such pneumatic tube system at the airport.

Hello Juan,
Thank you for contacting Denver International Airport. We have
  evaluated your email. I spoke with airport operations to find out if
  they had any information on using a pneumatic tube system and they
  advised me they do not. We do appreciate your feedback.
Thank you, kindly, for bringing this matter to our attention.
Warm Regards,
Flydenver Team  Meseret

Would you mind posting their full email reply? Thanks!

That means they are part of the conspiracy!   :-)))


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What does the zig-zag pattern on Hawker Hunter's leading edge represent?
On some Hawker Hunters, there is a zig-zag on the leading edge of the wing, as shown below.

Why do only some Hawker Hunters have this feature, and what is it for?

most military dog fighters have unconventional design choices for better response,

As already answered, the zigzag is a dogtooth extension or leading-edge extension on the outboard portion of the wing. It forces the airflow over the wing into a vortex, preventing spanwise flow outward along the wing at high angles of attack. A lot of modern designs incorporate them, including the horizontal tail of the F-15 Eagle, because they often have a side benefit of increasing airflow over the ailerons and increasing control.

To answer the second part of your question (why do only some Hawker Hunters have this feature?): the dogtooth extension wasn't incorporated into the design until the F.6 variant. Wikipedia's list of Hawker Hunter variants mentions it in a couple of entries.
Basically, the earlier models didn't have it; at some point the designers and aerodynamicists working on the Hunter tested it out.  Once they figured out that it was an improvement, they would have made the necessary changes to the production line to make it standard on all late-model aircraft built.

After doing a little more research I found the answer.
The zig-zag on the leading edge is a type of leading edge extension called a dogtooth extension.
Quote from wikipedia:

A dogtooth is a small, sharp zig-zag break in the leading edge of a
  wing. It is usually used on a swept wing, but also on straight wings
  ("Drooped Leading Edge" arrangement), to generate a vortex flow field
  to prevent separated flow from progressing outboard at high angle of
  attack. The effect is the same as a wing fence.
Where the dogtooth is added as an afterthought, as for example with
  the Hawker Hunter and some variants of the Quest Kodiak, the dogtooth
  is created by adding an extension to the outer section only of the
  leading edge.

Cirrus incorporates this design into their wings as well. Quoting from their site:

The outboard section of the Cirrus wing flies with a lower angle of
  attack than the inboard section. When the inboard section, which
  produces much of the lift, stalls the outboard section, where the
  ailerons are, is still flying. The result is that a stalled Cirrus
  airplane can be controlled intuitively using aileron.

You wouldn't happen to know why not all pictures of Hawker Hunters show this feature?

My only guess is that not all customers requested the feature in their Hunter wings.  As with anything, there are tradeoffs, and some customers may have not liked the side-effects of this version of wing.

Update: The hawker hurricanes wings are better describes as dogtooth extension as flyingfisch points out.

These features are known as a Leading edge cuff and aims to reduce spin tendencies by delaying the onset of stall.

As an added piece of information, this feature may have something to do with the fact that the Hawker Hunter, for many years, was the only swept wing fighter that could be reliably recovered from an inverted spin.
For this reason the Empire Test Pilot School at Boscombe Down used one for advanced training purposes (and may still do so).


text:
I live near an airport and this morning a plane was circling the town 6 times
I live near an airport and this morning a plane was circling the town 6 times  but still was landing for few seconds but flying away again . And this thing happens often in our small city .Any opinions?

We'll need more details to definitively answer this. What airport, what time, any details of the aircraft etc. See the linked questions in the answer below to get an oidea of what is needed.

Sounds like someone was doing a touch-and-go landing. This is usually done when learning to fly an aircraft, to be able to practice a number of landings in a short time window. If there is a flight school at your local airport, this might explain why it happens a lot.
See also:

Why do planes sometimes make a touch-and-go?
Why is this commercial plane making this manoeuvre?

No i don't have flight school my town it's very small because of tourism we have airport .plus was a commercial flight

Pilots of commercial jets (airliners) need practice too. A quiet airport has plenty of opportunity for touch& go landing practices.

That's right. In fact, near my hometown there is a small regional airport (albeit with a quite long runway, since it's a former military airport), where Lufthansa used to do their A380 trainings, which was quite a sight for that area.

@ΝικαΑντρεεα My home airport is busy, so all the flight schools take their students to nearby airports for practice. And how do you know it was a “commercial” flight? If you mean it was a jet, they need training/practice too, or it could be a test flight after major maintenance.

authors: Νικα Αντρεεα


text:
Do the shock waves from a supersonic plane affect general aviation planes?
Are there any considerations to take into account when flying around supersonic aircraft? I know that wake turbulence from large aircraft can pose a threat to smaller planes. Is the same true of the shock waves generated by planes in supersonic flight?
For instance, do fighter pilots need to be aware of the shock waves caused by other fighter planes in the vicinity?

Great question!  I am far from an expert in supersonic flight, but according to this NASA chat transcript, Ed Haering (an aerospace engineer at NASA's Dryden Flight Research Center in Edwards, Ca. who I would consider to be an expert) answers just this question and says that it isn't a problem for other airplanes:

chetman1020: Do sonic booms ever disrupt other things in the air?
Ed: Sonic booms can temporarily dissipate or accentuate a "Sun-Dog," the small bit of a rainbow off to either side of the Sun
  caused by high altitude ice crystals. Aircraft are not affected by
  booms from other aircraft.

I would imagine you would still hear them (at least in light GA aircraft, which aren't very soundproof) which might shake an unsuspecting pilot up a bit. The explanation above makes sense though - it's just a transient pulse of pressure through the atmosphere.

@voretaq7 That's a good question, I wonder if they would hear it?


text:
For ADF, what is the point of phase shifting the loop or sense antenna before combining them to get the bearing of the NDB?
Why is there a need to phase shift the loop or sense signal by 90 degrees as after combining the loop and sense antenna reading, the direction of the NDB can be found by finding the maximum strength.

There is no phase shift here, this wording has another meaning. There is a 90° bearing change. See also How does the ADF null positions find where the NDB is?

Because we don't use the signal maximum for the bearing. we use the MINIMUM, ie the indent in the cardiod diagram. Using the maximum, look at the signal strength when on-bearing versus slightly off-bearing - there's not much difference making it hard to determine the actual bearing. But when using the minimum part of the cardiod, slightly off-bearing is noticeably different from on-bearing.


text:
What is the point of modulating an adf loop antenna output with a voltage switching source through a balanced modulator?
In the block diagram I found for the ADF system, there is a balanced modulator fed with the output signal from the ADF loop antenna and a 47Hz signal from a switching source. What does the output from this balanced modulator looks like and what is the point of doing this?


text:
Is pitot and static pressure brought up to cockpit of Antonov 225 for the instruments?
Onboard the Antonov An-225, was the pitot and static pressure brought to the cockpit for the instruments such as airspeed indicators etc,. Or did the An-225 use remote indication through the use of transmitters?

Like all large modern aircraft of that era, pitot and static pressure will have been fed to an air data computer. The information is then distributed electrically to the flight instruments.


text:
Is Styrofoam or Balsawood better for gliders?
I have a project that requires me to use either one of the materials. Which one of the materials is better to use?

in order for us to answer you, you'll have to define "better"

What kind of project are you doing? What size? What is your end goal? Balsawood is stronger but foam can resist crash landings during tests more easily

Better as in based on strength and whether it will affect flight performance (distance flown, etc.), this project's end goal is to make an unpowered glider with a minimum wing span of 30cm that can fly as far as possible in a straight line.

30 cm? you shoul probably go to drones.se and post it there then. and include a good explanation of what is "better" for you. "based on strength" does not mean much.

How will it be launched?

Good old balsa is generally better.  It is stronger for its weight than Styrofoam, stiffer, and offers variety in building.
Styrofoam is cheap, easily molded and easier to repair.  "Foamies" can be mass produced and are adequate as models with reinforcement such as carbon fibre rods. Several types of foam are available.
Combinations of balsa and foam are possible, such as a foam core with wooden skin.
But building up a truss core structure (lots of triangles), spars, and ribs with balsa instead will save weight and will be far stronger. Skin can be 1/32 " balsa, Monokote, or even doped paper.
Construction will more closely resemble that of a full scale aircraft.


text:
Is an aircraft considered experimental if built when having A&P licence?
I got my Airframe and Powerplant while in the Army 20 years ago, never used it after I got out. If I built an aircraft from scratch would it be considered amature experimental?

I'm no expert, but I believe that until it receives CAA approval, every aircraft is consider experimental. Even Dick Rutan's aircraft were consider experimental until they received regulatory approval.

If you haven't used your A&P in 20 years I doubt it would be considered valid.

A&P doesn't expire.... your just considered "not current" you have to have 6 months/1000 hours to be brought back to current under someone with an A&P so they can sign off on your work and hours.

When you complete the airplane the FAA issues you a "Repairman's Certificate" that gives you the authority of an AI regardless of whether you have an A&P or not.Subsequent purchasers of Experimentals can also get them now by taking a little course. The rules in Canada where I am are pretty liberal on that. All maintenance work, incl structural repairs and engine rebuilds, etc, are signed off by whomever's name is on the C of R, whether they are the original builder or subsequent owner. If I want to fly in transponder airspace, though, I have to have my encoder signed off by an AMO every 2 yrs.

@JohnK - as an subsequent owner of a experimental aircraft, I'd appreciate knowing more about the "little course" you're referring to to get a Repairman Certificate.

@user2070305 My mistake it only applies to Light Sport airplanes.  Amatuer builts still only give it to the original builder, so as subsequent purchaser you can do everything but the annual and you need an A&P (doesn't have to be an AI) to sign the annual.

Yes, even if you are a certified A&P, any aircraft you build from scratch or a kit is considered an "amateur built" experimental. Even long running kits like Vans RV series are considered experimental. All aircraft are experimental until they receive certification from the FAA, which isn't economic for home builts.
It's considered "amateur built" because to the FAA, there are two classes of build, a certified aircraft in an assembly process in a factory, and amateurs.

From a strict legal sense the person who constructs 51% of the airplane is the "manufacturer".

And the manufacturer requires a Manufacturer’s Certificate…

Talking 100% and thank you. Just wanted to be sure before I put my self in bankruptcy and tried to fly with untested wings.


text:
How AeroVironment's Switchblades steer their flight?
I'm very intrigued with how AeroVironment Switchblades: SW-300, and SW-600, steer their flight. There are plenty of images and animations and to my observation, none of the Switchblades have ailerons, elevators, or rudders. They have a vertical stabilizer and the rear wing can be considered as the horizontal stabilizer but, it seems, no control surfaces. So how do they steer their flight? do the switchblades use the oblique wing concept to control their flight path?

It looks like there’s some sort of aileron/flaperon on the front wings.

From the video, the larger of the two clearly has a rudder as well…

The ailerons of the Switchblade 300 Block 10 and Block 20 version are moveable. This can be clearly seen for example in this video, where they can be seen in their full up position. You can also make out that the ailerons are fitted with two springs  pushing them up, and two actuators pushing them down. Therefore roll control is definitely realized via these ailerons. Here is a picture of the aileron spring and actuators, taken from this thread. Note that this construction allows the deployment of the wings without a fixed link between ailerons and the actuators.

Pitch control is performed (IMO) in one of the following ways:

Either the elevators are in reality elevons and therefore control roll and pitch
Or the elevator is tilted as a whole. Therefore, the mechanism carrying the swiveling mechanism, springs and elevator wing is swiveled by an independent servomotor.

Although I cannot find a source or good photo/video to prove either one of these theories, I suspect that these are elevons. This would have the advantage of having only 2 actuators, meaning less failure points, less complexity at the cost of having less control over the aircraft which is probably acceptable.
As far as I can see, yaw control is passive.

As a control theorist, I strongly disagree. It might not make a difference for a human pilot, but it definitely reduces controlability of the system

Ok, makes sense now that I think about it.  One thing's for sure, with such an arrangement you can't use differential aileron (elevon) throw to counteract adverse yaw.  I used to run into this all the time when I did a lot of slope-soaring with radio-control models.  Guys would talk about how they were using differential elevon throw to reduce adverse yaw with their Zagi-style "flying wings".  (2 elevons were the only control surfaces.)   (ctd)

(ctd)  I kept telling them, "All you are doing is mixing in a pitch input.  It's nothing more and nothing less than deciding you are going to pull a little extra aft stick every time you make a roll input."  Usually they didn't believe me.

Yes that is true, lacking adverse yaw capability is probably the most prominent effect. But controlability is a pretty loose term. The lack of an evelope also results in a smaller control envelope which might cost you some performance. But apparently the effect is small enought that AeroViroment accepts this performance loss for lesser complexity. This is a bit odd, as I would excpect that the performance aspect would be more important...

Not wishing to get into extended discussion, might the deployment of one control surface not generate yaw?  Speaking mainly as a paraglider pilot where this is the primary method of instigating a turn, and paradoxically, owing to the low flying speed, the reverse of normal aileron behaviour (since a pg turns towards the lowered control surface).

Thiis is exactly what adverse yaw is: https://en.wikipedia.org/wiki/Adverse_yaw?wprov=sfla1

I've seen lots of R/C models with aileron and elevator control, no rudder, and as long as you don't slow down too much they fly pretty much like any other model.  They were fairly common back when the cost of servos was high, or 4-channel radio gear cost significantly more than 3-channel (up until the mid-1980s, give or take).

@ZeissIkon, that is true, I also flew such models, but I always wondered: These are "precision" guided munitions, right? Does it not hurt accuracy when you soly rely on passive stability around the yaw axis? Of course it would be easy enough to perform some simulations in order to answer this, but I havend done this...

@U_flow The Switchblade is a surveillance device, not a munition as such, and there's plenty of precision in knowing where it's at.  In my experience, you don't need rudder unless you're flying at high coefficient of lift where adverse drag is a large factor.  Get some speed on, and your aileron deflection is much smaller and adverse drag becomes negligible.  Builders/fliers also used to set up with aileron differential (more up than down) to reduce adverse yaw.

@ZeissIkon Your point about needing rudder might be true, but the switchblade drone is a loitering munition. It first observes its target before ramming itself into it (see https://en.wikipedia.org/wiki/AeroVironment_Switchblade). Thats also why it is equipped with explosives, hence my original question. But you are right, I still would like to see some analysis or simulation results to see just how much difference a moveable rudder really makes :)

The real answer:
All controls are located in fuselage. They use two pushers in fuselage to rotate/move ailerons down. Two springs on wings move them up.

Hello Saiti, welcome to Aviation.Stackexchange, that is a nice insight, but @armando did ask about control surfaces not the actuators. However I am interested, do you have a source for this?


text:
How does one learn to sky write?
It seems like skywriting would be pretty difficult to learn, since there doesn't seem to be any way to step back and see if you made a mistake. And yet people have been doing it since the early days of flying.
So here is my question: how does one go about learning to sky write, and are there any tools to make it easier (a ground mounted webcam with a panel mounted display was an idea that came to mind, have no idea how feasible that is)?

I would assume you start with a lot of training in formation flying, and probably a little acrobatic work, followed by lots of on-the-job training (assuming something like the GEICO SkyTypers - Single-Plane skywriting where you're drawing with a smoke trail is probably lots of acrobatic training and a little formation stuff)...

Try reading this article from businessweek.  It's going to give you an answer, but you're probably not going to like it.  Here a quote:

“It requires an incredible level of precision flying,” Oliver says. “There are so many factors. Where’s the sun, which way is the wind blowing, where’s your crowd? You only learn that over time, after doing it enough. And you can’t go practice when skywriting fluid is 10 [dollars] a gallon and gasoline is 7 [dollars] a gallon.”
  It’s also difficult to learn the craft of skywriting when nobody is willing to teach it. Oliver and Asbury-Oliver won’t share any of their secrets. In fact, while Asbury-Oliver was employed by Pepsi, she was contractually forbidden from discussing her skywriting techniques with anybody, including friends, colleagues, and journalists. “In the ’30s and ’40s, there were a lot of skywriters trying to make a living,” she says. “So they shared nothing. They wouldn’t tell each other what kind of fluid they used to make the letters, what kind of exhaust pump they used. Everything was top secret.” While an air of secrecy might’ve made sense a century ago, why do they continue to be clandestine, despite their competition being essentially nonexistent? “We’re old enough and we’ve been around long enough that we’re both traditionalists,” says Oliver.

hmm, so you don't learn, you just are good at it or you aren't lol. And no one is gonna teach you either. Wow.


text:
Why is a sweeping second hand required for IFR?
The reasons why a clock is necessary for IFR have been explained elsewhere, but I haven't seen the reason that the clock has to have a sweeping second hand.
It seems like when timing things it would be more useful to have a ticking second hand, why is it expressly required that it be a sweep?

From what I can find, a "sweep-second hand" means that it is concentric with the hour and minute hands, not that it has to have a certain motion.

As @fooot mentions in the comments it means that the hand must be concentric with the hour and minute hands, it is not a reference between the difference of deadbeat and sweep seconds as many watch brands commonly reference now. This is a regulation that is intended to clarify the difference between a second hand that references the main dial and one that is on a sub dial. Historically planes may have had more complicated nav clocks like this hamilton where the large second hand is for the chronometer and not the elapsed time clock.

(source)
You can find what looks like one of the early AC's on digital clocks here. It references FAR 91.33 (which seems to no longer be in place) you can find the original verbiage here. I can not find any FAA legal interpretation that further defines "sweeping seconds".
On a bit of a side note, wrist watches (in any form) are not a legal substitute for a mounted clock.

The link to the letter re: wristwatches 404s, but the internet archive has a copy here

In IFR flight you sometimes need to accurately time seconds for approaches or turns.
Early watches did not have a "seconds" hand. Some watches had a small secondary dial for seconds, but because of the small size it was hard to read. The rule was written "sweep-second hand" meaning a seconds hand that swept around the main dial so that a pilot could accurately time seconds.
As "fooot" says above, it does not refer to the type of motion the hand makes.
I have seen some aircraft equipped with digital clocks and often wondered if I needed to wear a "sweep-second hand" watch to be legal.
Photo Source

I have seen some aircraft equipped with digital clocks and often wondered if I needed to wear a "sweep-second hand" watch to be legal. Unless your watch is installed equipment on the aircraft, it still wouldn't matter. I believe (but don't know for sure) that would mean you add your watch to the aircraft's weight and balance data.

@SteveV. According to this legal interpretation from the FAA, wrist watches are not a legal substitute for a mounted clock.

But digital presentations are legal even without a second hand.

Here is the ruling on using a watch (can't) but you can use an installed GPS or other Digital Clock. https://www.faa.gov/about/office_org/headquarters_offices/agc/pol_adjudication/agc200/Interpretations/data/interps/2016/Nkugba%20-%20(2016)%20Legal%20Interpretation.pdf Another installed appliance with a permanent clock display that meets the requirements of § 91.205(d)(6) that displays "hours, minutes, and seconds with a sweep-second pointer or digital presentation," is adequate for the purposes ofthis regulation.

FWIW, local DPEs and the FAA FSDO agree that a digital clock with a seconds display may be used as an equivalent of an analog clock with a "sweep second" pointer.  This was a big deal, perhaps in the 80's, but everyone has come to accept the digital clock as acceptable for flight operations and flight tests.
The point about a clock aircraft mounted is a MEL / 91.213 issue that should be understood by wanna-be instrument pilots. Practically, installed GPS satisfies the clock requirement.


text:
What vertical speed at touchdown makes a 'perfect' landing?
Is there a general vertical speed that pilots shoot for, or is it entirely by feel/trial-and-error?

-1 FPM, but it takes a looonngggg runway!  ;-)

I was just going to with 0 :) impossible?

@Lnafziger: yeah, but I was looking for a more typical FPM that passengers still consider soft

@flyingfisch I know, but "perfect" is "perfect"!  ;-)  (Don't mind me, I'm just trying to be funny.)

@Lnafziger: lol, that's fine, I was just wondering if maybe you had a realistic answer to give or not. ;-)

@p1l0t That's what I thought initially too but then realized that you couldn't land!  ;-)

This doesn't talk about fpm, but an interesting read nonetheless:  THE QUEST FOR THE PERFECT LANDING.  Bob Hoover says that you need a wet runway to get a perfect landing!

@p1l0t Theoretically the maths says you could land with zero vertical velocity.  Consider the shape of the curve height=x^2.  When x is zero (touchdown point) the rate of change in height is also zero (dh/dx = 2*x ), but only at the instant x=0.  If you are out by any amount either way you either don't touch down, or you land harder.  However real life also has other things to take into consideration that means this will never be practical.  Such as transitioning from wheels touching the ground with zero force to all lift dumped ready for breaking.  Or simply lumps in the runway.

Actually, it's perfectly possible to land at zero vertical speed. In fact, it's possible to land with a slightly positive vertical speed. All you need is a runway that is sloped upwards. :)

There is a bit of discrepancy between simulation and real world here. Simulator obviously knows vertical speed at any instant while accurately simulating the shock struts response is hard because the exact properties are hard to get (the manufacturer knows them, but does not usually publish them). On the other hand in real life temporal resolution of vertical speed indicator is not sufficient to get accurate value at touchdown while peak acceleration is easier to measure, and risk of damage depends on the peak acceleration, so that is what is used.

Are you talking the approach-to-land, or actual landing?   Keep in mind, when you flare, you are technically arresting a descent, so the VSI should not read much more/less than zero.
For a stable approach, 500-700 FPM on a 3 degree glide slope usually works out well for ILS approaches.  Keep in mind, all instrument approaches terminate visually, unless you are in a CAT III capable aircraft, which I do not fly.

I would argue that the way to think of the perfect landing is not in terms of vertical speed but rather in terms of the G-forces involved.
Thinking in terms of G-force, the perfect force depends on what you're landing on and how long it is. The various conditions I can think of offhand are:

long dry runway, no wind or straight down the runway -- try for a greaser if you want, although arguably a greaser is not the safest landing.
cross wind -- the higher the xwind the more you want a firm touchdown.
short runway -- firm so you will have effective braking.
wet runway -- firm, especially if the runway has standing water. The two times that I blew tires on landing was when there was standing water and I didn't plant it firmly enough. In the first case the tires blew before I used the brakes. It was an F27 and one of our pilots was in back at a window seat. He said the two right wheels never rotated at all. I had touched down with a greaser on a puddle.
carrier -- I once checked out a Navy carrier pilot in a 182. It was really hard for him to flare for a landing, since they don't do that. As I remember, he said that they wanted a 4G landing impact.

Lol at the carrier pilot, totally understand that! But they definitely land exactly where they want to!

The G-force experienced also depends on the shock-absorbing qualities of your mains, so it might be hard to figure out from the vertical speed, and it will definitely depend on the aircraft. Good answer!

@roe You're right, and as I think about it, it would not be an easy relationship to define mathematically, at least not for me. I edited out the last part of that first sentence.

Larger aircraft require a higher vertical velocity or impact to deploy Autobrakes and Spoilers. It depends on surface as mentioned by @Terry and on aircraft type.

Why would the tires explode on a wet runway if you didn't touch down hard enough?

@JayCarr It's hard to explain something I don't fully understand myself, but here goes. A too-smooth touchdown on a wet runway, especially if you touch down on standing water, fails to provide enough friction to start the tire rotating as the tire isn't really in contact with the runway. It's called dynamic hydroplaning. AS the aircraft continues, it's essentially surfing, and, as counter-intuitive as it might sound, the tire surface in contact with the water is super-heating. Finally, the superheated part of the tire fails.

I object to the concept of a Carrier pilot "landing" - no Carrier pilot has ever landed an aircraft, they simply crash it very accurately.

In my experience it's feel/trial-and-error-and-error-and-error.
5 feet off the runway is not a good time to be looking at your VSI.

Edit
Since you're looking at a record of your vertical speed after the fact:
Lower numbers are better of course. The goal is to get the rate low enough that the landing gear can absorb the impact without passing on any of the energy. 60 FPM would be 1 foot/second. I'm sure most landing gear would soak that up and earn you praises from your passengers.
I've had exactly one "squeeker" - I didn't know I'd touched down until the wheels started moving.  Naturally, I was in a single seat airplane with no witnesses :-(

Yeah, actually I was wondering so I could analyze my landings in a flight sim. It tells me my touchdown FPM after each flight. ;-)

Hmm. Lower numbers are better of course.  The goal is to get the rate low enough that that landing gear can absorb the impact without passing on any of the energy.  60 FPM would be 1 foot/second.  I'm sure most landing gear would soak that up and earn you praises from your passengers.

if you want to edit your answer with that information I can accept it ;-)


text:
Why does an aircraft have to be flying straight and level to facilitate a jump?
In the other questions about parachutes on this site, it has been stated that the aircraft would have to be flying straight and level to facilitate a jump. However, there were quite a few pilots during WWII whose planes were not flying straight and level and who still managed to escape.
Is there a difference between then and now that I am not catching?

I would add that a lot of the WWII pilots did not escape as well, and this is part of why we say that it should be straight and level.

One of the reasons why many WW2 pilots did not make it out were the G-forces and acceleration in directions other than the door when they had to get out. The bailing out survival rate appears to be correlated to the ease of exit.
If you're going to have a smooth and safe departure, you're happiest doing it during level flight when there's no interference from plane motion.

(source: lonesentry.com)

Note that you don't necessarily have to be flying straight and level: you could conceivably be in a controlled turn, climb, and maybe even a slight descent and still get out (the key is "controlled", and not subject to crazy acceleration/G loading). For a novice jumper though straight-and-level unaccelerated flight is the safest jump configuration, and the one most likely to result in a successful egress.

Is there any context for the second photo? I'm not sure what it illustrates aside from a plane you wanna bail out of.


text:
Is it legal to land in bad visibility conditions without ILS?
Korean Air Flight 801 crashed during bad visibility conditions in Guam because the ILS was out of commission and the pilot thought it wasn't.
My question though is why he even tried to land there in the first place. Wouldn't an airport be closed during bad visibility conditions in that scenario? Or is it possible to land without ILS in bad weather conditions?
I seem to remember someone talking about a step-chart or something like that as an alternative to ILS, is that what would be used in a case like that?

"Why he even tried to land there in the first place" - isn't that obvious? He thought he ILS was working.

ILS is just one of many different instrument approach types

The answer is "Maybe".
An ILS is actually comprised of two signals - a localizer (which lines you up with the runway) and a glideslope (which guides your vertical descent).
If the glideslope is out of service (as it was when KAL801 was flying its approach) you fly a localizer-only approach, which requires visual contact with the runway at a higher altitude.
In this case as shown on the plate below the ILS can be flown down to 531 feet (in red); the Localizer-Only approach can only be flown down to 1440 feet (in green).

So as long as the crew had the minimum visibility and cloud height requirements (and observed the altitude restrictions on the approach) they could legally fly into the airport on a localizer-only approach

In the case of KAL801 there were a few contributing factors to the accident (go ahead and skip to page 142, unless you really like reading NTSB reports):

The glideslope may have been receiving false signals.
The crew should have disregarded the glideslope indication anyway as it was NOTAM'd out of service, but it's possible the crew followed the needle anyway.
The DME fix for the approach is not located at the airport.
This may have caused the crew to believe they were closer to the airport than they actually were.
Because of (1), (2), or some other reason, the crew flew below the Localizer-Only minimum altitude.
This is ultimately why they hit the hill -- they were too low during the approach.
Had they been at or above the localizer-only minimum altitude they would have cleared the obstacles.

Note that this approach was changed post-crash -- it used to use the UMZ DME, but that's what likely confused the KAL crew.  Now, there's a DME colocated with I-GUM that yields a more sensible set of readings (i.e. ones that don't go to 0 and back up again as you head towards the runway).  Also, if you make sure you cross the BOLFY fix (aka 5.1 DME or right over the UMZ VOR) at or above 1440, you can go down to 980' ASL without the glideslope or being visual to the runway.

Airports don't typically close because of visibility.  In fact, ATC won't stop a pilot from flying an approach just because the weather is below minimums.  There are a couple of reasons for this:

The determining factor for landing is flight visibility, which may be different from the ground visibility that ATC has access to.  Under US Part 91 rules, a pilot may fly an approach even when the reported weather is below minimums, and if they have the required flight visibility and are in a position to land, they are allowed to land.  Part 121/135 operators aren't even allowed to try the approach though. ATC does not have to query the pilots to see which rules apply to them.  They assume that they won't ask for/accept a clearance if they aren't allowed to.
Different aircraft have different equipment and different pilots/operators have different training and rules.  For instance, one operator may be approved to use a Heads Up Display to land when the visibility is below landing minimums for another operator that does not have one.  ATC assumes that the pilot knows what they are doing and will only do what is legal for them.

As far as this specific case, @JayCarr has done a good job of answering what heppened here.  The pilots simply flew the approach incorrectly....

In regards to the title of your question (which is a little bit different from the body of your question), each approach has the minimum flight visibility listed for it at the bottom of the approach plate.  Unless specific authorization is received to reduce the visibility (as in the HUD example above), no it is not legal to land if the visibility is below minimums.
Each approach procedure also lists minimum altitudes that you may fly to at various points during the approach.  If an ILS is out of service, there is very often another type of approach that may be flown that usually prevents the pilot from descending as far.
A very common type of approach plate will have an ILS approach combined with a Localizer approach.  Since an ILS is made up of a localizer for horizontal guidance and a glideslope for vertical guidance, if the glideslope becomes inoperative then the localizer can still be used on its own.  A localizer only approach without vertical guidance, uses "step-down fixes" to indicate when descents are allowed.  Basically, you determine when one of these fixes is crossed and you are now allowed to descend to the next minimum altitude.  From the side it looks kind of like a staircase with the last "step" being flown visually in order to land.
An example of the bottom portion of an ILS or LOC approach plate:

I'll add to this where CatII and CatIII approaches exists ATC doesnt clear you specifically for those variants. They only trust that you are legal to land in the current conditions.

This is also a much better example of the step-down chart on an approach plate (since it has a bunch of steps on it :)

@voretaq7 That's why I picked this chart.  I've flown this approach a few times and entry time I just shake my head!

In the case of Flight 801 the pilot was using a DME system.  This is basically a series of transponders that tell you how far away they are located, and you figure your position based on how far you are from the DME and how that correlates to their position on your charts.  You also have a step chart that tells you how far from the runway they are and what altitude you should be at when you get to the DMEs.
What happened with flight 801 is that the pilots were not aware that the Guam airport had it's final DME about 3 miles short off the threshold, instead of right at the end of the runway. They thought the last DME was just about where they were supposed to land (faulty training, it would seem).  When they got close to the ground and finally broke the clouds they realized their mistake and tried to do a go around, but the engines couldn't spool up in time...  They basically just landed 3 miles short of the runway.


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Why don't airliners use full throttle on takeoff?
It seems that you would use full power for takeoffs, but when I have heard of airline pilots using less than full power on takeooff. Wouldn't it be safer to use full throttle?

See: http://aviation.stackexchange.com/questions/1627/is-it-possible-that-derated-thrust-takeoffs-are-safer-than-normal-takeoffs

ah, I didn't see that question. just voted to close this one


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Is it better to increase speed in a climb?
In straight and level flight, lift is determined by speed and angle of attack.  If we are heavier, we must go faster to generate more lift, at the same angle of attack.  At the same speed, angle of attack must be increased for more lift, hence the saying "stall speed increases with weight".
We know lift is less than weight in a descent, because the drag vector has a vertical component opposite weight.
We know lift = weight in level flight.
We know the wing is much more efficient than the prop at producing lift.  By simply raising the nose in a condition of 2400 lbs weight and 600 lbs thrust, sin angle × 600 obviously does not equal 2400 - cos angle × 2400.
We know in a climb there is a vertical component opposite lift.
Does this not in effect make the plane "heavier"?
Does this not allow us to keep optimal AOA, and steady state (not curving up or down) flight, at a slightly higher airspeed when climbing?
Should we not pitch to a slightly higher airspeed in a climb for maximum aerodynamic efficiency?

@ymb1 fair enough, this question is a more refined version, dealing with an increased vertical force requirement in a climb.  Do you think that statement is true or false.  This discussion continues because many points of view are correct.

Now, based on the $Lift$ equation, will a plane flying at its best AOA require more or less speed to create more vertical force and even if I double my thrust from 300 to 600 lbs, does that make up for 4x less efficiency than the wing?  Have a look at Quiet Flyers Cessna 152 chart.  Tell me how else it would be that way?

We know in a climb there is a vertical component opposite lift.
Does this not in effect make the plane "heavier"?
Does this not allow us to keep optimal AOA, and steady state (not
  curving up or down) flight, at a slightly higher airspeed when
  climbing?

No, a plane is in effect "lighter" in a climb than in level flight.
Climbing "unloads" the wing-- the lift vector is smaller in a steady climb than in level flight
For any given angle-of-attack, the airspeed must be lower in a steady climb than in level flight.
And for any given airspeed, the angle-of-attack must be lower in a steady climb than in level flight.
In a sustained vertical climb, lift must be zero, with thrust supporting the entire aircraft weight (and also overcoming drag).
Covered in detail (including vector diagrams) here-- Does lift equal weight in a climb?

Note: the question stated that the goal was to maximize "aerodynamic efficiency".  This would seem to imply that the goal is minimize fuel burn per altitude gain, or something similar.  Assuming that the engine is equally efficient at all airspeeds, it would seem that this would be achieved by maximizing the L/D ratio, in which case the concepts stated above are relevant.  Since angle-of-attack is tied to L/D ratio, any shift in the correlation between airspeed and angle-of-attack will change the airspeed that we should fly at, although the shift may be too small to notice in actual practice.  For shallow climb angles the Lift vector is really only reduced by a very small amount, and since Lift for a given angle-of-attack varies according to airspeed squared, the resulting shift in the airspeed associated with a given angle-of-attack will be quite small.
While it's good to understand the basic physics at play, we should be clear that in actual practice, it is by no means always optimum to climb at an airspeed that is lower than the airspeed corresponding to the attack that yields the maximum L/D ratio in level flight.  It depends on what parameter we are trying to optimize and on what other variables are at play.  In most aircraft, these other variables will produce changes in the optimum airspeed for climbing that completely dwarf the slight shift in the relationship between angle-of-attack and airspeed that is caused by the "unloading" of the wing during the climb.
We are more often interested in climbing at the maximum possible rate, or the maximum possible angle, than we are in climbing in the most aerodynamically efficient manner.  Particularly in aircraft with piston engines, the difference can be enormous.
In theory, for a fixed amount of Thrust, the steepest climb will be obtained at the angle-of-attack that gives the highest possible L/D ratio, but this will not be the fastest climb.  Climb rate depends on the difference between power-available and power-required.  Even though the speed where minimum power is required is actually slightly below the best L/D speed, in an aircraft with a fixed-pitch prop the speed for best climb rate is usually above the best L/D speed, because of the greater power available when the engine can turn at a higher RPM.  On the other hand, since Thrust equals power divided by speed, in a piston-engine aircraft more Thrust will typically be available at low airspeeds than at high airspeeds, despite the loss of RPM.  Since climb angle depends on the difference between Thrust and Drag, in a piston-engine aircraft the steepest climb angle typically occurs at an airspeed a little below the airspeed that yields the maximum L/D ratio, i.e. at an airspeed a little below the airspeed that yields the minimum amount of Drag.  For general aviation light airplanes with piston engines, these kind of effects related to available Thrust or Power will usually have an effect on the airspeed that yields the maximum climb rate, as well as the airspeed that yields the maximum climb angle, that completely dwarfs the effect due to the slight "unloading" of the wing by the climb angle, and the resulting slight shift in the airspeed that is associated with any given angle-of-attack.
Example-- from this Cessna 152 data sheet--
Best climb angle 55 KIAS
Best glide speed 60 KIAS
Best L/D speed-- not stated
(Theoretical best L/D speed is slightly faster than best glide speed because the drag from the windmilling or stopped propeller biases the best glide speed to be slower than the best L/D speed.)
Best climb rate 67 KIAS

Related ASE questions on the relationship between Vx, V best-glide, and Vy:
How can best glide speed be lower than best rate of climb speed??
Is Vy closer to Vbg with a variable pitch prop

Best way to illustrate these things is to take them to an extreme by imagining the climb attitude getting steeper and steeper, and eventually the wing is completely unloaded and the propeller thrust is providing all the lift (assuming you have a thrust to wt >1:1).

@John K that's right, and you only reduce AOA when drag from wing exceeds vertical lift contribution, then it's all engine to climb.  The NF-104 story is a great one to read.  A great pilot wanted to use to wing, and may have wound up saving so much fuel it was too much weight for the rocket at the end.

Best rate of climb 67 KIAS, more thrust available at lower airspeed, points to less drag and/or more efficient use thrust, the wing. Viola!  But you are right in that the advantages are very slight, and quickly drowned out if one tries to go still faster.  I am interested in preserving optimal AOA for safety, if it can be done.

@RobertDiGiovanni -- "Best rate of climb 67 KIAS, more thrust available at lower airspeed, points to less drag and/or more efficient use thrust, the wing." -- actually I think it simply points to more POWER available at higher airspeed, due to more RPM available.

@RobertDiGiovanni -- I would like to see someone give a good answer to your older question https://aviation.stackexchange.com/questions/56084/is-vy-closer-to-vbg-with-a-variable-pitch-prop .  As I understand things the answer ought to be "yes" but I can't confirm from practical experience.

@quiet flyer yes, and perhaps the prop AOA is closer to optimal too.  Enough here to keep digging.


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When are what type of callsigns used?
Some callsigns are in the format (Something) "(Number)-(Number)". Other callsigns are in the format of one word, such as the famous examples of Pete "Maverick" Mitchell and Bradley "Rooster" Bradshaw. At what times are these callsigns used?

Section 2-4-20 of the 7110.65 describes how callsigns are to be used.
Tactical pilots of the US Navy and Airforce commonly give each other "callsigns", but they are actually just nicknames.  They are used only for inter-flight communication with other pilots on discrete squadron frequencies.  They are not used with ATC.

Ok, so here's what I think you meant: Take the example of a YouTuber and EA-18 pilot with the callsign "Pail" in VAQ-139. On the squadron frequency other squadron members would call him "Pail" but everywhere else he's just "Cougar (Number)-(Number)".

Something like that, yes. There are two possible definitions for the term "callsign:" 1) a nickname and 2) a formal identifier used by/with ATC. (See also my answer here.)

@JustACoder, yes, that's exactly what I meant.  Cougar in this case is their assigned squadron call sign, the number is generally the mission number per the flight schedule, but it may be the side number of the aircraft.


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What are the variants of the J-11 still used by China?
The J-11A Flanker-B+ is a Chinese licensed copy of the Su-27SK from Russia (Unlike the J-11B which wasn't). So do the PLAAF still use the J-11A (If so, with AL-31s or WS-10s?)

The J-11A was not a licensed copy, it was a joint assembly project. China tried to sell internationally but the engine performance leaves much to be desired. The J-11B is an illegal copy of the -11A, in keeping with China's bad habits of stealing IP from other countries.

@JuanJimenez  J-11 was a licensed copy of Su-27SK that was divided into two parts. Part A was to assemble locally with Russian parts, which last from 1996 to 2007 (first deliver of parts in 1996, first flight in 1998). Part B was to use locally made parts and started as soon as technical materials was received. The first B model took flight in 2003 and is in production till this day. If B were an illegal copy why would Russia have supplied engines and other parts for it for 20+ years?

@user3528438 It's what happens when you get caught making illegal copies. You ask for forgiveness after the fact and pay a license fee. Had China had the ability to produce good engines that would probably not have happened.

@JuanJimenez If it's all that simple then I'll start making illegal copies of everything myself.

@user3528438 Knock yourself out, but make sure you lawyer up first.

@user3528438 If you build the world's #1 economy and #2 military first, you just might get away with it.

@Therac China have gotten away with it numerous times but this is the a few cases where it's legit. There are licensed copies foreign car all over the streets.

The PLAAF still uses the J-11A. Some J-11As received some new missile approach warning systems and some upgrades to the fire-control system back in 2015 but since the J-11A is just a Su-27 assembled in China, even the upgraded J-11As probably still use the AL-31 engine.
Edit: The first 100 J-11s built use the AL-31, but the rest use the WS-10A.

Oh, ok. So are they still unable to carry the PL-8 and PL-12 Air-to-Air missiles?

Correct, it seems that they're still limited to R-77s and PL-10s.

So they were changed to carry PL-10s but not PL-8s or PL-12s?

As far as the article states, that's precisely the case. China's J-11As can't carry PL-8s or PL-12s, at least for now. The upgrades only appear to have added the ability to carry PL-10s and R-77s.

So do the Chinese still use the AA-11 Archer AAM or has it been totally replaced by the PL-10?

China still uses the AA-11 / R-73, although it's not compatible with the J-15, J-16 or J-20 (The J-10, Su-27 / J-11A, and Su-35 can use them) so they might be planning on retiring it at some point.

Okay, so they literally still use the old cockpit of the Su-27SK? If so that's interesting.

The J-11As were literally just Su-27SKs sold to China as kits. Given that the J-11B is a reverse-engineered version of the J-11A / Su-27SK, it wouldn't be that surprising if China reused the Su-27SK cockpit.

We know they reused it (Deka Ironworks Simulations found that out for DCS World) but do they still use the same cockpit?

The J-11B and J-11D have a glass cockpit, which the J-11A doesn't have. Other than this and some improved subsystems, the cockpit is probably still the same.

Oh, wow. That's very interesting.


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What is the N001VEP symbology in the Su-27SM?
I saw on Wikipedia that the N001VEP radar in the Su-27SM can track 10 targets at a time and engage 4 of them at a time.
So, what is the symbology of the N001VEP in the Su-27SM that allows it to do this? Because the base Su-27 has the radar symbology on the HUD, and it doesn't seem like this would be possible with radar symbology on the HUD.
Also, why can't they conceivably engage 10 targets at a time if they had missiles?

The question is a bit muddled…. How does symbology either “allow” or inhibit the number of targets being tracked?  Whether you choose “X” or “O” for the targets, or choose to display them on the HUD or main screen, isn’t this just a user interface decision made during software development?

"why can't they conceivably engage 10 targets": That's not a matter of interface, but of switching the radar from the pulse-Doppler mode used in tracking to the more resource-demanding CW mode required for missile homing.


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Questions about cockpits
I was looking at some plane cockpits, and I wondered something. We see the F-4 Phantom's cockpit below:
Obviously, very analog. Then, we entered a new era of cockpit design, where we had designs like this in the F/A-18E/F:

Very nice. However, we improved the cockpits further. Below are the cockpits of the F-35:

My question is: How is the F-35's cockpit better than the F/A-18E/Fs, and why did we even make the improvement?
Also, the F-35 has 55 buttons on its HOTAS system. Why does it have so many HOTAS-bound buttons when earlier jets like the aforementioned Super Hornet have less?

I don’t think it is that the display configuration is qualitatively better.  rather, it’s more flexible.  It allows that the software to present situation-specific information to the pilot better.  Imagine a situation where I needed to correlate information from one of the FA18’s displays with another display in the opposite corner.  A flexible display allows the software to present both pieces of information side by side…  or better yet, do the correlation itself and only present the pilot with the already-analyzed data, presented as decision points at the right time.

In terms of buttons on the HOTAS, is this not answered by the very concept of leaving pilots hands in one place https://en.wikipedia.org/wiki/HOTAS? Also note that F-35 photo appears to be a ground based trainer so may not represent an actual F-35 instrument setup, suspect the panels left and right of the display will have more clutter in an actual aircraft so final result may be less different.

Does the dashboard in your dads 1967 F-150 look the same as the dashboard in your 2023 Tesla? Both have a "steering wheel" and (mostly) the same pedals. But everything else is different.

There is important part of the F-35 instruments missing from that photo: the helmet-mounted display.

Yes I get that the HMDS is absolutely insane.

Re HOTAS -- it is not by random chance that the academies have decided to recruit woodwind / sax instrumentalists.

The trend in these modern cockpit designs is to improve flexibility and at the same time decrease cost and complexity. Ultimately you achieve this by moving more functionality to software.

Flexibility: A wide screen multi-function display (MDF) as seen in the F 35, can be easily partioned to display several displays at the same time, or use a 1/3 to 2/3 screen, or half half, etc. Additionally you do not loose the space taken by the frames if several displays are used as in the F/A 18. Therefore you can display more information. Also if you want to integrate new functionalites, a MFD easily offers this flexibility. Last but not least, the pilot can easily reconfigure his display to fit his/her needs however he/she wants, which also improves usability.
Decreased cost: It might be cheaper to have one singular screen which offers all functionality, then having to produce and maintain several specialized buttons and displays. Again this moves more complexity to software which might be cheaper then maintaining more hardware.
Complexity: Again, less hardware to maintain. If you want to integrate new buttons, all you have to do is to update the software. Of course in the aviation world this presents its own challenges, but is still easier then integrating new buttons or so.

Concerning the HOTAS buttons, this is to steer as many functions with your hands on stick and throttle. This way, the pilot does not have to take his/her hands off the stick when controlling functions of the airplane therefore posing less of a distraction to the pilot.

“My question is: How is the F-35's cockpit better than the F/A-18E/Fs, and why did we even make the improvement?
Also, the F-35 has 55 buttons on its HOTAS system. Why does it have so many HOTAS-bound buttons when earlier jets like the aforementioned Super Hornet have less?”
You’re looking at the evolution of 60 years worth of cockpit design in these photographs, not to mention 60 years of evolution in fighter aircraft design, missions systems, and capabilities.  One thing that is clearly visible in all of these photographs is the trending from the pilot as a stick and rudder guy to more of a weapon systems officer and a tactician. That is, cockpits and missions systems aboard modern fighter aircraft are handling much, much more of a routine and mundane aspects of flying an airplane and allowing the pilot to concentrate much more of his brain power on employing weapons, operating mission systems and concentration on the battle.  In contrast, the jet and the computer hardware and software aboard are handling most of the aspects of flying the aircraft and translating all sensory influence and systems information.  It can then display this onto easy to read, and understand, minimalist cockpit displays, which the pilot can call up and can set however he desires when is needed for a particular stage of a flight or mission.
As visible in a 1960s era F-4 cockpit, were computer power technology is nowhere near what it is today, all you could do was display the information, either on analog gauges or crude, monochrome CRT displays.  The pilot would have to digest that information and make decisions accordingly. Combat experiences in Vietnam showed that there was only so much brain power. A fighter pilot could be called up under stress and in combat to use. Excessive amounts of systems with simply saturate the individuals, and potentially cause them to overlook critical elements of the fight that could kill them.  General Robin Olds once commented that when they fenced in in Vietnam, i.e. crossing over in the enemy territory, that they actually started turning systems off in the F4 because they did more harm than good, and it allowed the pilot to concentrate on the battle better.
The F-18 cockpit is a classic example of lessons learned from the Vietnam conflict. Here computers have made considerable improvements in information crunching and can be used to handle many more tasks aboard. Other technologies, such as multi function displays, head-up displays and HOTAS controllers (a Hornet has about 40 or so buttons on the stick and throttle) helped digest more information and allow the pilot to better command the aircraft and its mission systems with his head out of the cockpit for better SA.  Take this one step further with the F-35 cockpit combined with blazing fast computers, all glass touchscreen displays, HMDs, encrypted networking between other friendly assets in the battle space and the aircrews have far more systems and capabilities with much more brainpower available to use them.  About 95% of the F-35 pilot’s activity in the cockpit can be concentrated on where he is and other assets are, where the enemy is, what threats are out there, how they are going to coordinate, and use their combine force to destroy them, and what weapons he wants to employ to do so.


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Why was the Pratt & Whitney F100 never put on the F-14 Tomcat?
Why was the Pratt & Whitney F100 never put on the F-14 Tomcat? The engine bays of jets like the F-15 and F-16 can accompany both the F100 and the GE F110. It would've been a quick solution to the underpowered and compressor stall-prone TF30 engine. So, why was the F100 never strapped onto the Tomcat?

Near as I know, it very nearly was used in the F-14B variant of the Tomcat but ultimately was downselected against after the failure of the Convair XFV-12 aircraft, which would have used the a predecessor of the F100 engine to power it.
Ultimately, the Navy went with the GE F110 engine in the F-14B & D variants.  Exactly why this decision was made in the 1980s is unknown. I suspect it was done, in part, because Navy Pentagon brass who flew the F-14As and had such a bad experience with the temperamental Pratt & Whitney TF-33 engines.  They contrasted that with GE’s ability to produce good naval fighter engines; case in point was the F404-GE-400 in the newer F/A-18 Hornets.

Pratt & Whitney got a contract for the F100-PW-100 and F401-PW-400 engines in 1970. The F401 was larger thrust with an extra stage in the compressor (on the fan shaft).
When the F-14 was started, the F100 and F401 engines were not yet available so they used the TF30 in F-14A with the assumption that the F-14B with F401 would follow shortly. DOD cancelled the F401 leaving the F-14 with the TF-30 for many years.
According to wikipedia (entry for Pratt & Whitney F401), "Due to costs and the reliability issues that dogged early F100s, the F401 was eventually cancelled in 1974".
There were a number of aircraft the engine might have been used on, including the Navy F-16 (Vought proposal jointly with General Dynamics, the Navy opted to go with F-18 based on YF-17) and Rockwell XFV-12 in 1977.

The F100-PW-100 was introduced in 1972, just 3 years after the F-14 was. So why exactly did they not quickly rush the F100 to the F-14? It had a bit less compressor stall issues, and could be a 2nd quick fix until better engines came along. The F-14A was in service until 2004 with VFA-211. That's a long time to not put better engines.


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Is dirigible cluster ballooning feasible?
Has steerable cluster ballooning with a propeller and fins/stabilizers of some sort ever been attempted? If not, would it really make sense at all, and what would the challenges be, as compared to a normal airship?
Since to be steerable the aircraft needs to have a somewhat stable shape, would perhaps fixing the multiple balloons with some bands or by some other mechanism help at all, given their stretchiness? Would the passing of air in between balloons affect flight characteristics negatively?
Maybe would it make more sense to cover the cluster of balloons with an outer, non gas-tight envelope? But that already reminds me of rigid airships, and the gas bags there were for some reason made not out of rubber but out of cow gut - I'm also wondering if rubber was  unsuitable for such an application, or if cow gut was more economical back then.

In the wide open experimental realm of the examples you cite, anything is feasible.  This isn’t a good question though, it’s more of an invitation to random musings…

The rules here (and everywhere on SE) call for a single question per post. Sometimes you can get away with 2 or 3 closely related questions. I count 5 question marks, and you end up talking about "cow gut" which seems quite unrelated to feasibility of cluster ballooning, but might make it if it was in its own question.

Answering the question in the title rather than the body - no it is not feasible in most cases.
The usefulness of a powered lighter than air craft hinges greatly on the useful payload VS drag. For a given lifting gas you want the minium amount of balloon skin holding it in, for a cluster balloon you end up with a fairly poor ratio of skin area to internal volume.
You also have issues with the balloons touching and rubbing together which is not good for extended flight, and a cluster of spheres will tend to make for a higher frontal area (higher drag) than a conventional design in a neat row with a aerodynamic shell.
There are cases where the ratio of needed balloon size to structure is low enough that it makes sense to have a beam with balloons spaced along them, such as  under water or non earthlike atmospheres but on earth, with the current atmosphere this does not make sense.
As you note, Zepplin style rigid designs ARE sort of cluster balloons since as size increases there are issues with 'sloshing' of the gas similar to water hammer that require increasing skin strength to manage, and also instability if too much of the lifting gas is free to move along the length of the craft so they are technically a row of balloons flying in very close formation, but constrained for stability and reduced wear.